Nutrient addition drives declines in grassland species richness primarily via enhanced species loss

Declines in grassland diversity in response to nutrient addition are a general consequence of global change. This decline in species richness may be driven by multiple underlying processes operating at different timescales. Nutrient addition can reduce diversity by enhancing the rate of local extinction via competitive exclusion, or by reducing the rate of colonization by constraining the pool of species able to colonize under new conditions. Partitioning net change into extinction and colonization rates will better delineate the long-term effect of global change in grasslands.
We synthesized changes in richness in response to experimental fertilization with nitrogen, phosphorus, and potassium with micronutrients across 30 grasslands. We quantified changes in local richness, colonization, and extinction over 8-10 years of nutrient addition, and compared these rates against control conditions to isolate the effect of nutrient addition from background dynamics.
Total richness at steady ...